The present invention relates to an image pickup apparatus having a photoelectric conversion function.
Image sensors of CCD (Charge Coupled Device), CMOS (Complementary Metal-Oxide Semiconductor), and the like are required that their dynamic range should be widened with high sensitivity and a high S/N (Signal-to-Noise) ratio maintained. As image pickup apparatuses whose dynamic range can be widened, for example, the following technologies are known.
In the technology disclosed in Japanese Unexamined Patent Publication No. 2006-217410 (Patent Document 1), each pixel of an image pickup apparatus includes the following: a photodiode, a transfer transistor, a floating diffusion (floating area), an overflow gate, a storage capacitor, a reset transistor, a storage transistor, an amplification transistor, and a select transistor. (Refer to FIG. 1 in the document.)
The photodiode receives light and generates and stores photocharges. The transfer transistor is provided adjacently to the photodiode and transfers photocharges generated at the photodiode. The floating diffusion is coupled to the photodiode through the transfer transistor. The overflow gate is provided adjacently to the photodiode to transfer photocharges overflowing the photodiode in storage operation. The storage capacitor stores photocharges overflowing the photodiode in storage operation through the overflow gate. The reset transistor is so formed that it is coupled to the floating diffusion and discharges signal charges in the storage capacitor and the floating diffusion. The storage transistor is provided between the floating diffusion and the storage capacitor. The amplification transistor reads as voltage the signal charges of the floating diffusion or the signal charges of the floating diffusion and storage capacitor. The select transistor is coupled to the amplification transistor and selects a pixel or a pixel block.
In the technology disclosed in Japanese Unexamined Patent Publication No. 2006-245522 (Patent Document 2), each pixel of an image pickup apparatus includes the following: a photodiode, a transfer transistor, a floating diffusion, first and second storage capacitors, a reset transistor, first and second storage transistors, an amplification transistor, and a select transistor. (Refer to FIG. 1 in the document.)
The photodiode receives light and generates photocharges. The transfer transistor is provided adjacently to the photodiode and transfers photocharges generated at the photodiode. The floating diffusion is so provided that it is coupled to the photodiode through the transfer transistor. The first and second storage capacitors store photocharges overflowing the photodiode in exposure storage operation through the transfer transistor. The reset transistor is so formed that it is coupled to the first storage capacitor and discharges signal charges in the first storage capacitor, second storage capacitor, and floating diffusion. The first storage transistor is provided between the floating diffusion and the first storage capacitor. The second storage transistor is provided between the first storage capacitor and the second storage capacitor. The amplification transistor reads as voltage the signal charges of the floating diffusion, the signal charges of the floating diffusion and the first storage capacitor, or the signal charges of the floating diffusion, first storage capacitor, and second storage capacitor. The select transistor is coupled to the amplification transistor and selects a pixel or a pixel block.